A current triple-shade roller blind generally includes a curtain having two soft fabric layers reeled on a reel shaft in a headrail for achieving a great variety of light and dark effects, as compared with conventional Venetian style blinds and single cloth blinds. Such roller blind is typically controlled by a manual force or by means of a bead chain to wind up or unwind the curtain. To further adjust the shading effect of the aforesaid roller blind, such as that disclosed in Taiwanese Patent Publication No. M503854, a control mechanism is employed and operated with a bead chain that hangs down to a lower position for facilitating operation. Such bead chain poses choking or strangulation hazards to young children.